Fiber optic jumper cable

ABSTRACT

A fiber optic jumper cable having a central axis includes a bend-resistant optical fiber generally arranged along the central axis. A tensile-strength layer surrounds the bend-resistant optical fiber. A protective cover surrounds the tensile-strength layer and has an outside diameter D O  in the range 1.6 mm≦D O ≦4 mm.

RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.12/603,131 filed Oct. 21, 2009, which is incorporated by referenceherein in its entirety.

BACKGROUND

1. Technical Field

The present disclosure relates generally to fiber optic cables, and inparticular relates to a fiber optic jumper cables having an opticalfiber.

2. Technical Background

Conventional fiber optic cables include optical fibers that conductlight for transmitting voice, video and/or data. The construction offiber optic cables should preserve optical performance when deployed inthe intended environment while also meeting the other additionalrequirements for the environment. Mechanical requirements orcharacteristics, such as crush performance, permissible bend radii,temperature performance, and the like, are preferred to inhibitundesirable optical attenuation or impaired performance duringinstallation and/or operation within the space in which the fiber opticcable is deployed.

Fiber optic cables that connect optical devices over relatively shortdistances (e.g., up to a few meters) are referred to in the art as“patch cords” or “jumper cables,” or just “jumpers” for short. Jumpersare often used to form cross-connections between terminated opticalfibers. For example, jumpers are used to connects ports within a fiberdistribution frame (FDF), which is a telecommunications device in theform of a large panel having interconnected fiber terminations atcorresponding ports.

Because jumpers are relatively short, they typically employ multimodeoptical fibers. Certain types of jumpers are intended for outdoor use,such as in network access points (NAPs) and network interface units(NIUs). Because space is limited in FDFs, NAPs, NIUs and liketelecommunication devices, it is preferred that the jumpers not only beflexible, but have the ability to be sharply bent so that the amount ofspace they occupy is as small as possible. Unfortunately, most jumperscannot tolerate significant bending because the light traveling thereinwill be attenuated beyond allowable limits. In fact, many types ofjumpers have strength elements embedded therein to prevent the jumperfrom bending beyond a select bending radius. This reduces the ability ofthe jumper to fit within a tight space, thereby requiring thetelecommunication device in which the jumper is used to be sized toaccommodate the relatively bend-sensitive jumper.

SUMMARY

An aspect of the disclosure is a fiber optic jumper cable having acentral axis. The cable includes a bend-resistant multimode opticalfiber generally arranged along the central axis, and a tensile-strengthlayer surrounding the bend-resistant optical fiber. A protective coversurrounds the tensile-strength layer and has an outside diameter D_(O)in the range

1.6 mm≦D_(O)≦4 mm.

Another aspect of the disclosure is a fiber optic jumper cable thatincludes a bend-resistant multimode optical fiber generally axiallyarranged along the cable central axis and having a nominal outsidediameter of 900 microns, and a core having a nominal diameter of 50microns. The cable includes a tensile strength layer immediatelysurrounding the bend-resistant optical fiber. A protective coverimmediately surrounds the tensile strength layer and has an outsidediameter D_(O) in the range 1.6 mm≦D_(O)≦4 mm.

Another aspect of the disclosure is a method of forming a fiber opticjumper cable having a central axis. The method includes disposing abend-resistant multimode optical fiber generally along the central axis,and surrounding the bend-resistant optical fiber with a tensile-strengthlayer. The method also includes surrounding the tensile-strength layerwith a protective cover having an outside diameter D_(O) in the range1.6 mm≦D_(O)≦4 mm.

It is to be understood that both the foregoing general description andthe following detailed description present embodiments of thedisclosure, and are intended to provide an overview or framework forunderstanding the nature and character of the disclosure as it isclaimed. The accompanying drawings are included to provide furtherunderstanding of the disclosure, and are incorporated into andconstitute a part of this specification. The drawings illustrate thevarious example embodiments of the disclosure and, together with thedescription, serve to explain the principles and operations of thedisclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is fragmentary isometric view and

FIG. 2 is a cross-sectional view of an example fiber optic jumper cableaccording to one example embodiment;

FIG. 3 is a side view of an example jumper comprising the jumper fiberoptic jumper cable of FIG. 1 but with connectorized ends;

FIG. 4 is a schematic fragmentary side view of the jumper connecting twoports of a telecommunications device while being tightly coiled in anarrow space;

FIG. 5 is a side view of an example bend-resistant multimode opticalfiber used in example embodiments of the fiber optic jumper cabledisclosed herein;

FIG. 6 is a schematic representation (not to scale) of a cross-sectionalview of the bend-resistant multimode fiber of FIG. 5;

FIG. 7 shows an example schematic representation (not to scale) of therefractive index profile for the cross-section of FIG. 6, wherein thedepressed-index annular portion is offset from the core by an innerannular portion and is surrounded by an outer annular portion;

FIG. 8 is a plot of the change in attenuation (“Δ attenuation”) in dBversus bend radius in mm for a standard 50 micron multimode fiber and a50 micron bend-resistant multimode fiber at wavelengths of 850 nm and1,300 nm;

FIG. 9 is a plot of the modeled Δ attenuation in dB versustime/temperature at wavelengths of 850 nm and 1,300 nm for a fiber opticjumper cable having standard multimode fiber and for an example fiberoptic jumper cable of the present disclosure; and

FIG. 10 is a cross-sectional view similar to FIG. 2, and shows anexample “zipcord” type fiber optic jumper cable that utilizes twoside-by-side cables with a common protective cover.

DETAILED DESCRIPTION

Reference is now made in detail to the present preferred embodiments ofthe disclosure, examples of which are illustrated in the accompanyingdrawings. Whenever possible, identical or similar reference numerals orsymbols are used throughout the drawings to refer to identical orsimilar parts. It should be understood that the embodiments disclosedherein are merely examples with each one incorporating certain benefitsof the present disclosure. Various modifications and alterations may bemade to the following examples within the scope of the presentdisclosure, and aspects of the different examples may be mixed indifferent ways to achieve yet further examples. Accordingly, the truescope of the disclosure is to be understood from the entirety of thepresent disclosure in view of, but not limited to the embodimentsdescribed herein.

In the discussion below, the terms “fiber optic jumper cable” and“cable” refer to an unconnectorized cable, while the term “jumper”refers to a connectorized cable, i.e., a cable having at least oneconnector.

FIG. 1 is a fragmentary isometric view and FIG. 2 is a cross-sectionalview of a fiber optic jumper cable (“cable”) 10 according to oneembodiment. Cable 10 can have other configurations, although the cableof FIG. 1 and FIG. 2 is described in more detail hereinbelow forpurposes of illustration. Cable 10 is suitable, for example, for forminga jumper used in telecommunication devices such as FDFs, and inparticular is useful for outdoor telecommunication devices such NAPs,NIUs and like outdoor units of a telecommunications system or network.

Cable 10 has a central axis A1 and includes a bend-resistant multimodeoptical fiber (“BR-MM fiber”) 20 arranged generally along the centralaxis. An example BR-MM fiber 20 has a nominal outside diameter D₂₀=900microns and has a core 21 with a nominal diameter D_(C)=50 microns.Example BR-MM fibers 20 are described in greater detail below.

Cable 10 also includes a tensile-strength layer 30 that surrounds BR-MMfiber 20. In an example embodiment, tensile-strength layer 30immediately surrounds BR-MM fibers 20, as shown. In an exampleembodiment, tensile-strength layer 30 comprises at least one ofwater-blocked stranded aramid yarn, super-absorbing polymer (SAP),SAP-coated filaments, fiberglass, and like elements used in cables toachieve water blocking and/or tensile-strength enhancement.Tensile-strength layer 30 also serves as a cushioning layer thatprotects BR-MM fiber 20.

Cable 10 also includes a protective outer layer in the form of a cablejacket 50 that surrounds tensile-strength layer 30. In an exampleembodiment, cable jacket 50 immediately surrounds tensile-strength layer30, without any intervening layers or elements. Cable jacket 50 can beformed of various materials, but in example embodiments is formed from athermoplastic elastomer such as polyethylene (PE). Plastics such aspolyvinyl chloride (PVC) may be used, but such plastics tend to degradewith age and exposure to the elements so that their use for outdoorapplications is not typically preferred. Cable jacket 50 may be formedof other types of plastics, including flame retardant polyethylene(FRPE), fluoro-plastics, such as PVDF, fluoro-compounds as disclosed byU.S. Pat. No. 4,963,609, and blends of PVC and PVDF or PVC and PE. Cablejacket 50 may also be formed from combinations of the above-identifiedmaterials.

While polyurethane is a very good material for cable jacket 50 in termsof resistance to cold temperatures, ruggedness and shrinkage, it is alsopresently about $10/kg and thus about ten times more expensive than PE.Thus, embodiments of the invention include a cable jacket 50 comprisingPE and a cable jacket 50 that consists solely of PE. When the cablejacket 50 is said to comprise polyethylene, it is understood that othercompositions may be present in the cable jacket in smaller amounts thanpolyethylene. For the purposes of this specification, a “polyethylenejacket” is formed of at least 80% polyethylene.

In an example embodiment, cable jacket 50 is designed to have increasedburn resistance such that the fiber optic cable has a riser, a plenumand/or a low smoke zero halogen rating. In this regard, cable jacket 50can include aluminum trihydrate, antimony trioxide or other additivesthat increase the burn resistance of the cable jacket as known to thoseskilled in the art, and as described by U.S. Pat. No. 6,167,178.Additionally, cable jacket 50 can be designed to be resistant to UVlight, which is desirable for outdoor applications.

Three example sizes of cable 10 include an outside D₀=1.65 mm with cablejacket thickness T₅₀=0.18 mm; an outside D₀=2 mm with cable jacketthickness T₅₀=0.25 mm; and an outside D₀=3 mm with cable jacketthickness T₅₀=0.5 mm. An example thickness T₅₀ for cable jacket 50 is inthe range 0.15 mm≦T₅₀≦0.55 mm, with T₅₀=0.25 min being an exemplarythickness. An example cable 10 has an outside diameter D_(O) in therange 1.6 mm≦D_(O)≦4 mm, with D_(O)=2.0 mm (nominal) being an exemplaryoutside diameter suitable for many applications.

Fiber optic cables for outdoor use have traditionally used polyethylenefor the cable jacket since it is moderate in cost but performsreasonably well in harsh environments where the cable is exposed to coldtemperatures, ultraviolet (UV) exposure, abrasion and impacting forces.However, because PE generally undergoes significant amounts of shrinkagedue to aging and exposure to cold temperatures, conventional cables withPE jackets included one or more anti-buckling strength elements.Anti-buckling elements were used because buckling or bending leads tobending of the optical fiber within the cable, which in turn causesattenuation of light traveling in the optical fiber. An exampleanti-buckling strength element for a conventional jumper is rigid, suchas a glass-reinforced plastic (GRP) rod. Typical GRP rods have adiameter between 1.25 mm to 2.05 mm, and add to the cost and complexityof manufacture, as well as increasing the bend radius of the cable. Thecable embodiments according to the present embodiments are constructedsuch that PE jacketing materials are used without the requirement ofanti-buckling elements. For example, the cables can be free of GRP rodsand other anti-buckling elements. This allows the fiber or fibers in thecables to be generally aligned with the cable centerline. As its nameimplies, tensile-strength layer 30 only provides protection fromtensioning forces and does not provide substantial anti-buckling(including anti-bending) strength.

FIG. 3 is a side view of an example embodiment of a connectorized cable10, i.e., a jumper 11 having connectors 60 at each end. Example types ofconnectors 60 include SC, FC, LC and ST connectors. FIG. 3 shows twoFC-type connectors 60 by way of example. In an example embodiment,connector 60 simply comprises a ferrule. In an example embodiment,connectors 60 include respective strain-relief boots 62 that allow cable10 to have a substantial bend at the base of each connector. In anexample embodiment, jumper 11 is connectorized only at one end.

FIG. 4 is a schematic fragmentary side view of jumper 11 used to form across-connection within a telecommunications device 70.Telecommunication device 70 has a surface 72 with connection ports 74configured to mate with connectors 60. Telecommunications device 70 alsoincludes a front door 76 that defines a narrow space 78 between thefront door and device front surface 72. Jumper 11 is showncross-connecting two ports 72 within narrow space 78. Because jumper 11includes BR-MM fiber 20, it can be tightly coiled to fit into the narrowspace 78 since severe bends 80 associated with the coil do notsubstantially impact the performance of the jumper. This allows fornarrow space 78 to be smaller than is possible with prior art jumpers,thereby allowing for a smaller telecommunications device 70.

Another benefit of using a BR-MM fiber 20 is that it is less susceptibleto shrinkage of cable jacket 50 effects due to relaxation of residualextrusion stress therein and also due to expansion and contractionattendant with temperature variations. These effects can producesubstantial bends in cable 10 that do not impact BR-MM fiber 20 asadversely as they would non-bend-resistant optical fiber.

Bend-Insensitive Multimode Fibers

As discussed above, cable 10 includes a BR-MM fiber 20. FIG. 5 is a sideview of an example BR-MM fiber 20, which has a central axis or“centerline” AC. FIG. 6 is an example cross-sectional view of BR-MMfiber 20 of FIG. 5. FIG. 7 shows a schematic representation of therefractive index profile BR-MM fiber 20. BR-MM fiber 20 has a glass core21 and a glass cladding 22, the cladding comprising an inner annularportion 23, a depressed-index annular portion 24, and an outer annularportion 25. Core 21 has outer radius R1 and maximum refractive indexdelta Δ1MAX. The inner annular portion 23 has width W2 and outer radiusR2. Depressed-index annular portion 24 has minimum refractive indexdelta percent Δ3MIN, width W3 and outer radius R3. The depressed-indexannular portion 24 is shown offset, or spaced away, from the core 21 bythe inner annular portion 23. Annular portion 24 surrounds and contactsthe inner annular portion 23. The outer annular portion 25 surrounds andcontacts the annular portion 24. The clad layer 22 is surrounded by atleast one coating 26, which may in some embodiments comprise a lowmodulus primary coating and a high modulus secondary coating. An exampleBR-MM fiber 20 is the CLEARCURVE multimode fiber, available fromCorning, Inc., Corning, N.Y.

An example inner annular portion 23 has a refractive index profile Δ2(r)with a maximum relative refractive index Δ2MAX, and a minimum relativerefractive index Δ2MIN, where in some embodiments Δ2MAX=Δ2MIN. Anexample depressed-index annular portion 24 has a refractive indexprofile Δ3(r) with a minimum relative refractive index Δ3MIN. An exampleouter annular portion 25 has a refractive index profile Δ4(r) with amaximum relative refractive index Δ4MAX, and a minimum relativerefractive index Δ4MIN, where in some embodiments Δ4MAX=Δ4MIN.Preferably, Δ1MAX>Δ2MAX>Δ3MIN. In some embodiments, the inner annularportion 23 has a substantially constant refractive index profile, asshown in FIG. 7 with a constant Δ2(r); in some of these embodiments,Δ2(r)=0%.

In some embodiments, the outer annular portion 25 has a substantiallyconstant refractive index profile, as shown in FIG. 7 with a constantΔ4(r); in some of these embodiments, Δ4(r)=0%. The core 21 has anentirely positive refractive index profile, where Δ1(r)>0%. Radius R1 isdefined as the radius at which the refractive index delta of the corefirst reaches value of 0.05%, going radially outwardly from thecenterline AC. Preferably, the core 21 contains substantially nofluorine, and more preferably the core 21 contains no fluorine. In someembodiments, the inner annular portion 23 preferably has a relativerefractive index profile Δ2(r) having a maximum absolute magnitude lessthan 0.05%, and Δ2MAX<0.05% and Δ2MIN>−0.05%, and the depressed-indexannular portion 24 begins where the relative refractive index of thecladding first reaches a value of less than −0.05%, going radiallyoutwardly from the centerline. In some embodiments, the outer annularportion 25 has a relative refractive index profile Δ4(r) having amaximum absolute magnitude less than 0.05%, and Δ4MAX<0.05% andΔ4MIN>−0.05%, and the depressed-index annular portion 24 ends where therelative refractive index of the cladding first reaches a value ofgreater than −0.05%, going radially outwardly from the radius whereΔ3MIN is found.

BR-MM fiber 20 may comprise a graded-index core 21 with cladding 22surrounding and directly adjacent the core, with the cladding comprisingdepressed-index annular portion 24 having a depressed relativerefractive index relative to another portion of the cladding. Thedepressed-index annular portion 24 of cladding 22 is preferably spacedapart from core 21. Preferably, the refractive index profile of the core21 has a parabolic or substantially curved shape. The depressed-indexannular portion 24 may, for example, comprise: a) glass comprising aplurality of voids, or b) glass doped with one or more downdopants suchas fluorine, boron, individually or mixtures thereof. Thedepressed-index annular portion 24 may have a refractive index deltaless than about −0.2% and a width of at least about 1 micron, with thedepressed-index annular portion being spaced from the core 21 by atleast about 0.5 microns.

In some embodiments, BR-MM fiber 20 comprises a cladding with voids, thevoids in some preferred embodiments are non-periodically located withinthe depressed-index annular portion. “Non-periodically located” meansthat if takes a cross section (such as a cross section perpendicular tothe longitudinal axis) of BR-MM 20, the non-periodically disposed voidsare randomly or non-periodically distributed across a portion of thefiber (e.g. within the depressed-index annular region). Similar crosssections taken at different points along the length of the BR-MM fiber20 will reveal different randomly distributed cross-sectional holepatterns, i.e., various cross sections will have different holepatterns, wherein the distributions of voids and sizes of voids do notexactly match for each such cross section. That is, the voids arenon-periodic, i.e., they are not periodically disposed within the fiberstructure. These voids are stretched (elongated) along the length (i.e.generally parallel to the longitudinal axis) of the optical fiber, butdo not extend the entire length of the entire fiber for typical lengthsof transmission fiber. It is believed that the voids extend along thelength of the fiber a distance less than about 20 meters, morepreferably less than about 10 meters, even more preferably less thanabout 5 meters, and in some embodiments less than 1 meter.

BR-MM fiber 20 exhibits very low bend-induced attenuation, and inparticular very low macrobending induced attenuation. In someembodiments, high bandwidth is provided by low maximum relativerefractive index in the core, and low bend losses are also provided.Consequently, BR-MM fiber 20 fiber may comprise a graded index glasscore 21; and an inner cladding 23 surrounding and in contact with thecore, and a second cladding 24 comprising a depressed-index annularportion surrounding the inner cladding, said depressed-index annularportion having a refractive index delta less than about −0.2% and awidth of at least 1 micron, wherein the width of said inner cladding isat least about 0.5 microns and the fiber further exhibits a 1 turn, 10mm diameter mandrel wrap attenuation increase of less than or equal toabout 0.4 dB/turn at 850 nm, a numerical aperture (NA) of greater than0.14, more preferably greater than 0.17, even more preferably greaterthan 0.18, and most preferably greater than 0.185, and an overfilledbandwidth greater than 1.5 GHz-km at 850 nm. By way of example, thenumerical aperture for BR-MM fiber 20 is between about 0.185 and about0.215.

In an example embodiment, core 21 has a 50 micron diameter (nominal).Such BR-MM fibers 20 can be made to provide an overfilled (OFL)bandwidth of greater than 1.5 GHz-km, more preferably greater than 2.0GHz-km, even more preferably greater than 3.0 GHz-km, and mostpreferably greater than 4.0 GHz-km at an 850 nm wavelength. By way ofexample, these high bandwidths can be achieved while still maintaining a1 turn, 10 mm diameter mandrel wrap attenuation increase at an 850 nmwavelength of less than 0.5 dB, more preferably less than 0.3 dB, evenmore preferably less than 0.2 dB, and most preferably less than 0.15 dB.These high bandwidths can also be achieved while also maintaining a 1turn, 20 mm diameter mandrel wrap attenuation increase at an 850 nmwavelength of less than 0.2 dB, more preferably less than 0.1 dB, andmost preferably less than 0.05 dB, and a 1 turn, 15 mm diameter mandrelwrap attenuation increase at an 850 nm wavelength, of less than 0.2 dB,preferably less than 0.1 dB, and more preferably less than 0.05 dB.

Such BR-MM fibers 20 are further capable of providing a numericalaperture (NA) greater than 0.17, more preferably greater than 0.18, andmost preferably greater than 0.185. Such fibers are furthersimultaneously capable of exhibiting an OFL bandwidth at 1300 nm whichis greater than about 500 MHz-km, more preferably greater than about 600MHz-km, even more preferably greater than about 700 MHz-km. Such fibersare further simultaneously capable of exhibiting minimum calculatedeffective modal bandwidth (Min EMBc) bandwidth of greater than about 1.5MHz-km, more preferably greater than about 1.8 MHz-km and mostpreferably greater than about 2.0 MHz-km at 850 nm.

Preferably, BR-MM fiber 20 exhibits a spectral attenuation of less than3 dB/km at 850 nm, preferably less than 2.5 dB/km at 850 nm, even morepreferably less than 2.4 dB/km at 850 nm and still more preferably lessthan 2.3 dB/km at 850 nm. Preferably, BR-MM fiber 20 exhibits a spectralattenuation of less than 1.0 dB/km at 1300 nm, preferably less than 0.8dB/km at 1300 nm, even more preferably less than 0.6 dB/km at 1300 nm.

In some embodiments, the core 21 extends radially outwardly from thecenterline AC to a radius R1, wherein 10 microns≦R1≦40 microns, morepreferably 20 microns≦R1≦40 microns. In some embodiments, 22microns≦R1≦34 microns. In some preferred embodiments, the outer radiusof the core 21 is between about 22 to 28 microns. In some otherpreferred embodiments, the outer radius of the core is between about 28to 34 microns.

In some embodiments, the core 21 has a maximum relative refractiveindex, less than or equal to 1.2% and greater than 0.5%, more preferablygreater than 0.8%. In other embodiments, the core has a maximum relativerefractive index, less than or equal to 1.1% and greater than 0.9%.

In some embodiments, BR-MM fiber 20 exhibits a 1-turn, 10 mm diametermandrel attenuation increase of no more than 1.0 dB, preferably no morethan 0.6 dB, more preferably no more than 0.4 dB, even more preferablyno more than 0.2 dB, and still more preferably no more than 0.1 dB, atall wavelengths between 800 and 1400 nm. Example BR-MM fibers 20 arealso disclosed in U.S. patent application Ser. Nos. 12/250,987 filed onOct. 14, 2008, and 12/333,833 filed on Dec. 12, 2008, the disclosures ofwhich are incorporated herein by reference.

FIG. 8 is a plot of the change in attenuation (“Δ attenuation”) in dBversus bend radius in mm for standard 50 micron multimode fiber and a 50micron BR-MM fiber 20 at wavelengths of 850 nm and 1,300 nm. The bendradius was established using two wraps around mandrels having radii of4.2 mm, 5.4 mm and 10.4 mm. A bend test around a 120 mm diameter mandrelas used to model projected attenuation for both the standard multimodefiber and BR-MM fiber 20. The data indicate that the BR-MM fiber 20provides about a 4× attenuation benefit at 850 nm and about a 2× benefitat 1,300 nm over standard multimode optical fiber.

Using the bend-loss information from FIG. 8, the projected performancefor cable 10 when exposed to temperature cycling was modeled BR-MM fiber20. The model compared bending effects from the model results shown inFIG. 8 to actual test data for a standard cable with 50 micron multimodefiber that was tested for a potential application as a security cameracable. FIG. 9 is a plot of “Δ attenuation” in dB versus time/temperaturefor a D_(O)=3 mm polyethylene cable with standard 50 micron (corediameter) multimode optical fiber and the same cable but with a 50micron BR-MM fiber 20.

The reduction in cable attenuation seen for MM-BR fiber 20 meetsindustry standards ICEA-596 and GR-409 for multimode fiber of ≦0.6 dB/kmat a temperature of −40° C. for outside plant cables. These attenuationrequirements are utilized when designing optical telecommunicationsystems to ensure that loss budgets are achieved.

Additional performance gains can be obtained by optimizing the jacketingprocess through fiber-strain control and tolling draw optimization tocontrol shrinkage.

Additionally, the performance of cables 10 is such that they can beutilized for longer distances. One such example application is as asecurity camera cable. A typical security camera installation may use aduplex jumper also known as a “zipcord.” FIG. 10 is a cross-sectionalview similar to FIG. 2, except it shows an example zipcord duplex-typefiber optic jumper cable 10′ made up of two cables 10 having commonouter jacket 50′. Common outer jacket 50′ is formed by two outer jackets50′ joined via a connecting portion 51′. Common outer jacket 50′ istypically simultaneously extruded over the two cable 10 so that itincludes connecting portion 51′.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the present disclosurewithout departing from the spirit and scope of the disclosure. Thus, itis intended that the present disclosure cover the modifications andvariations of this disclosure, provided they come within the scope ofthe appended claims and their equivalents.

We claim:
 1. A fiber optic jumper cable having a central axis,comprising: a bend-resistant optical fiber generally arranged along thecentral axis, wherein the bend resistance of the optical fiber is suchthat: with one turn around a 10 mm diameter mandrel, the bend-resistantoptical fiber exhibits an attenuation increase of less than 0.5 dB at awavelength of 850 nm; with one turn around a 15 mm diameter mandrel, thebend-resistant optical fiber exhibits an attenuation increase of lessthan 0.2 dB at a wavelength of 850 nm; and with one turn around a 20 mmdiameter mandrel, the bend-resistant optical fiber exhibits anattenuation increase of less than 0.1 dB at a wavelength of 850 nm; atensile-strength layer surrounding the bend-resistant optical fiber; anda protective cover surrounding the tensile-strength layer and having anoutside diameter DO in the range 1.6 mm≦DO≦4 mm, wherein the protectivecover is a protective outer layer in the form of a cable jacket, whereinthe protective cover comprises polyethylene, and wherein the protectivecover is formed from at least 80% polyethylene.
 2. The fiber opticjumper cable of claim 1, wherein the tensile-strength layer comprises atleast one of aramid yarn, fiberglass and super-absorbent polymer.
 3. Thefiber optic jumper cable of claim 1, wherein the protective cover has athickness T50 in the range 0.15 mm≦T50≦0.55 mm.
 4. The fiber opticjumper cable of claim 1, wherein the cable jacket is formed from flameretardant polyethylene.
 5. The fiber optic jumper cable of claim 1,wherein the cable has an outside diameter in the range of 1.6 mm to 4mm.
 6. The fiber optic jumper cable of claim 1, wherein the cable doesnot include anti-buckling elements and wherein the tensile strengthlayer provides protection from tensioning forces but does not providesubstantial anti-buckling strength or anti-bending strength.
 7. Thefiber optic jumper cable of claim 1, wherein the bend resistance of theoptical fiber is such that: with one turn around a 10 mm diametermandrel, the bend-resistant optical fiber exhibits an attenuationincrease of less than 0.3 dB at a wavelength of 850 nm; with one turnaround a 15 mm diameter mandrel, the bend-resistant optical fiberexhibits an attenuation increase of less than 0.1 dB at a wavelength of850 nm; and with one turn around a 20 mm diameter mandrel, thebend-resistant optical fiber exhibits an attenuation increase of lessthan 0.05 dB at a wavelength of 850 nm.
 8. A fiber optic jumper cablehaving a central axis, comprising: a bend-resistant optical fibergenerally arranged along the central axis, wherein the bend resistanceof the optical fiber is such that: with one turn around a 10 mm diametermandrel, the bend-resistant optical fiber exhibits an attenuationincrease of less than 0.5 dB at a wavelength of 850 nm; with one turnaround a 15 mm diameter mandrel, the bend-resistant optical fiberexhibits an attenuation increase of less than 0.2 dB at a wavelength of850 nm; and with one turn around a 20 mm diameter mandrel, thebend-resistant optical fiber exhibits an attenuation increase of lessthan 0.1 dB at a wavelength of 850 nm; a layer surrounding thebend-resistant optical fiber; and a protective cover surrounding thelayer and having an outside diameter DO in the range 1.6 mm≦DO≦4 mm,wherein the protective cover is a protective outer layer in the form ofa cable jacket, wherein the protective cover comprises polyethylene, andwherein the protective cover is formed from at least 80% polyethylene.9. The fiber optic jumper cable of claim 8, wherein the layer comprisesat least one of aramid yarn, fiberglass and super-absorbent polymer. 10.The fiber optic jumper cable of claim 8, wherein the protective coverhas a thickness T50 in the range 0.15 mm≦T50≦0.55 mm.
 11. The fiberoptic jumper cable of claim 8, wherein the cable jacket is formed fromflame retardant polyethylene.
 12. The fiber optic jumper cable of claim8, wherein the cable has an outside diameter in the range of 1.6 mm to 4mm.
 13. The fiber optic jumper cable of claim 8, wherein the cable doesnot include anti-buckling elements and wherein the layer providesprotection from tensioning forces but does not provide substantialanti-buckling strength or anti-bending strength.
 14. The fiber opticjumper cable of claim 8, wherein the bend resistance of the opticalfiber is such that: with one turn around a 10 mm diameter mandrel, thebend-resistant optical fiber exhibits an attenuation increase of lessthan 0.3 dB at a wavelength of 850 nm; with one turn around a 15 mmdiameter mandrel, the bend-resistant optical fiber exhibits anattenuation increase of less than 0.1 dB at a wavelength of 850 nm; andwith one turn around a 20 mm diameter mandrel, the bend-resistantoptical fiber exhibits an attenuation increase of less than 0.05 dB at awavelength of 850 nm.
 15. A fiber optic jumper cable having a centralaxis, comprising: an optical fiber generally arranged along the centralaxis; a tensile-strength layer surrounding the optical fiber; and aprotective cover surrounding the tensile-strength layer and having anoutside diameter DO in the range 1.6 mm≦DO≦4 mm, wherein the protectivecover is a protective outer layer in the form of a cable jacket, whereinthe protective cover comprises polyethylene, and wherein the protectivecover is formed from at least 80% polyethylene.
 16. The fiber opticjumper cable of claim 15, wherein the tensile-strength layer comprisesat least one of aramid yarn, fiberglass and super-absorbent polymer. 17.The fiber optic jumper cable of claim 15, wherein the protective coverhas a thickness T50 in the range 0.15 mm≦T50≦0.55 mm.
 18. The fiberoptic jumper cable of claim 15, wherein the cable jacket is formed fromflame retardant polyethylene.
 19. The fiber optic jumper cable of claim15, wherein the cable has an outside diameter in the range of 1.6 mm to4 mm.
 20. The fiber optic jumper cable of claim 15, wherein the cabledoes not include anti-buckling elements and wherein the tensile strengthlayer provides protection from tensioning forces but does not providesubstantial anti-buckling strength or anti-bending strength.